Automotive engine carburetors conventionally include a vacuum break assembly which opens the carburetor choke blade to a vacuum break position after the engine is started. The vacuum break assembly includes a diaphragm which responds to engine vacuum and, when engine vacuum increases after the engine is started, pulls the choke blade to the vacuum break position.
Some vacuum break assemblies include an adjusting screw which limits the travel of the diaphragm in response to the increase in engine vacuum. The screw provides a stop for the diaphragm and is adjusted to establish the vacuum break position of the choke blade.
It will be appreciated that such an assembly should be sealed against air leaks which might otherwise disturb the engine vacuum signal which operates the vacuum break assembly. Thus in previous constructions, the adjusting screw was sealed by an O-ring, and an elongated sealing surface was required to maintain a seal about the screw over its range of adjustment.